Phosphazenes are chemical compounds containing the following structural unit in which the free valences can be occupied by various groups. ##STR2## A variety of phosphazene compositions and methods of preparation are known in the art. U.S. Pat No. 3,291,865 to Kober, et al. discloses non-flammable, hydrolytically stable phosphazene compositions for use as hydraulic fluids, lubricants and additives. These phosphazenes carry an aryloxy and a fluoroalkoxy substituent and are synthesized by forming the alkali metal salt of the fluorinated alcohol followed by reaction of that salt and a phenolic salt with a phosphonitrilic chloride.
Lederle, et al, J. Chem. & Eng. Data, Vol. 11, No. 2, April 1966, page 221 discloses fire resistant hydraulic fluids made in a manner similar to Kober et al. Ottmann et al, Ind. & Eng. (Chem. Prod. Res. & Dev.), Vol. 5, No. 2, June 1966, page 202 describe arylamino fluoroalkoxy-substituted phosphonitrilic cyclic trimers.
Singler et al, "Army Science Conference Paper", A117298 sets forth the synthesis and evaluation of phosphazene fluids in an attempt to find a replacement for triarylphosphates under military specification MIL-H-19457c. This research involved the use of trifluoroethoxy-substituted cyclic phosphonitrilates which were also substituted with either m-chlorophenoxy or m-trifluoromethylphenoxy groups.
Singler, "Potential of Phosphazenes as Hydraulic Fluids", Hydraulic Fluids Meeting, NASA Ames Research Center, February 1976 summarizes the effect of various substituents on the substituted cyclic phosphonitrilic trimers and tetramers.
More recently, Singler et al, Ind. Eng. Chem. (Prod. Res. & Dev.), Vol. 25, No. 1 (1986) describe hydraulic fluids made by substituting cyclic phosphonitrilic chloride with both aryloxy groups and trifluoroethoxy groups.
Carr, Eur. Pat. Appl. No. 0 145 002, published June 19, 1985 discloses a phosphazene fluid prepared by reacting cyclic phosphonitrilic chloride trimer with a phenol, a fluoroalcohol or mixtures thereof.
Fluoroalkoxy-substituted phosphazenes also are disclosed in U.S. Pat. No. 3,304,350 to Kober, et al. These highly fluorinated materials have a high flash point and display acceptable low-temperature properties in hydraulic fluid applications. A variety of other phosphazene compositions are known in the art. U.S. Pat. No. 3,370,020 to Allcock, et al, U.S. Pat. No. 3,505,087 to Godfrey, U.S. Pat. No. 4,081,593 to Lanier, U.S. Pat No. 4,018,967 to Roller, et al, U.S. Pat. Nos. 4,110,421, 4,157,425 and 4,116,891 to Dieck, et al, U.S. Pat. No. 3,990,900 to Franko Filipasic, et al and U.S. Pat. No. 3,545,942 to Rice, et al disclose phosphazenes which may be substituted by a variety of alkoxy, arylalkoxy or aryloxy groups.
Most recently we have disclosed in U.S. Pat. No. 4,698,439 a method for preparing phosphazene hydraulic fluids that remain solids-free on storage at temperatures down to -30.degree. C. These materials have fluoroalkoxy as well as substituted and unsubstituted aryloxy substituents on the phosphonitrilic backbone.
While many of the prior art phosphazene fluids are fire resistant, having a relatively high flash point, unacceptable low temperature properties restrict their utility. Further, because of the high concentrations of fluorine required, the cost of the resulting phosphazene hydraulic fluid is very high when compared to conventional fluids.